How common is life in the universe? Nobody can say. The problem is that when we address the question, we have a sample of exactly one biome. Which means that any conclusions we draw have a standard deviance of plus or minus infinity.
But we can make a pretty good statistical stab at how many Earth-sized planets there are circling Sol-like suns within the "Goldilocks zone," where it's neither too hot nor too cold for large amounts of liquid water to exist on the surface.
CBC News reported, about a month and a half ago, that a recent study took a Kepler telescope study of a slice of 42,000 stars in our galaxy, crunched numbers, and then extrapolated for the entire Milky Way Galaxy. There are roughly 200 billion stars in the MWG, of which 40 billion are pretty much like our own sun. Based on what they saw, the scientists estimate that 22 percent of those stars have Earth-like planets that could harbor life.
Using numbers a little more precise than those cited above, that comes to 8.8 billion Earthlike worlds in the Milky Way Galaxy alone. Which is, as Carl Sagan liked to point out, only one of billions and billions of galaxies in the universe.
What does this mean as far as the existence of life goes? Well, when you have a paper published in Proceedings of the National Academy of Science, you're not allowed to make wild surmises. Which is why there are science fiction writers.
And so, by the awesome power invested in me as a science fiction writer, I am able to say: God is not only good but also generous. The galaxies are green.
Somewhere out there, right now, somebody on a planet you've never seen is wondering if we exist too.
You can read the article here. Or you can just go outside tonight and stare at the stars in silence.